<form action="{ $BASE_URL }" method="post">
    <input class="return" type="hidden" name="return" value="" />
    <input type="hidden" name="todo" value="search" />
    <input type="text" name="q" id="departement" class="search_field" required />
</form>

{literal}
<script>
    autoComplete = {
        element : '#departement.search_field',
        data : {
            serviceUrl: '{ /literal }{ $SYS_FOLDER }{ literal }services/autocomplete/departement/',
            minChars: 2,
            deferRequestBy: 300,
            onSelect: function(value, data){ submitQuery('#departement.search_field', value,data); }
        }
    }
</script>
{/literal}